The present invention relates to a projection-type display device using a light collecting plate, and more specifically to a display panel associated with the light collecting plate in a predetermined positional relationship and a position adjusting method for the display panel.
Hitherto, many types of liquid crystal display panels have been proposed. The most commonly used type of liquid crystal display panel is one that has a layer of liquid crystal represented by twisted nematic liquid crystal. With this type of liquid crystal display panel, display is achieved by controlling the twist of liquid crystal molecular orientation to determine the optical rotatory power of light that passes through the liquid crystal layer. Stated in more detail, the operating principle consists in the control of light transmission to the image observed surface side of the liquid crystal display panel by employing the birefringence or optical rotatory power of light in the liquid crystal layer and the linear polarization characteristics of the polarizing plates.
The liquid crystal display panel has thin film transistors (hereinafter referred to as TFTS) each formed for the purpose of switching a voltage applied to the liquid crystal within an associated pixel. The TFTs made of amorphous silicon or polysilicon have been manufactured or are now under development. Among them, the polysilicon-based TFTs have advantages resulting from the mobility in polysilicon. That is, in the first place, since the polysilicon is high in mobility, the amount of charge that can be flowed into each TFT per unit time can be increased. Therefore, the TFT size can be reduced and, as a result, the pixel aperture ratio can be increased. Second, a circuitry of driving the switching TFTs can be formed on the same substrate using polysilicon. Accordingly, the necessity of driver ICs serving as the driving circuitry and the mounting step therefor is eliminated, reducing the manufacturing cost. Further, it is possible to reduce the width of the frame portion outside the display area, which will be required in a future liquid crystal display panel. Because of the aforementioned advantages, attention has been paid to the polysilicon-based TFTs as a key technology.
A liquid crystal display panel containing the driving circuitry formed of such polysilicon TFTs has been developed and manufactured as a display element for a video projector or a video camera monitor because it provides a small, high-definition display panel.
In order to attain high brightness, the video projector generally employs a three-panel scheme of displaying a color image with three liquid crystal display panels for red, green and blue (hereinafter referred to as R, G, and B, respectively) which are three primary colors of light. On the other hand, the video camera monitor employs a single-panel scheme of displaying a color image with a single liquid crystal display panel having a color filter. In addition, a low-brightness projector has been manufactured by diverting the single liquid crystal display panel for the video camera monitor to projection.
However, the liquid crystal display panel for the single-panel scheme requires three times as many pixels as that for the three-panel scheme. When the display panel for the single-panel scheme is formed in the same size as that for the three-panel scheme, the aperture ratio thereof is lowered due to the required number of pixels. In addition, there is loss of light due to the color filter. Therefore, it is difficult to implement a high-brightness projector. For this reason, the three-panel scheme is mainly employed in the conventional projector. However, it difficult to reduce the manufacturing cost since three display panels and an optical separation and collection system are required in the three-panel scheme.
In view of a reduction in the manufacturing cost, attention has been paid on new types of single-panel projectors. In particular, a single-panel projector that uses dichroic mirrors for performing deflection and color separation and a liquid crystal display panel having a microlens light collecting plate, and a single-panel projector that uses a liquid crystal display panel having a hologram optical element plate for performing color separation and light collection are being developed actively.
FIG. 14 schematically illustrates the operating principle of a liquid crystal projector that requires no color filter, and FIG. 15 illustrates the paths of light incident on a set of RGB pixels in the liquid crystal projector. As shown in FIG. 14, a microlens light collecting plate 102 is mounted on the light receiving surface of a liquid crystal display panel 104, which is composed of an array substrate 105 having TFTs formed thereon and a counter substrate 106 opposed to the array substrate. The light collecting plate 102 has an array of microlenses 102L each assigned to a corresponding set of RGB pixels on the liquid crystal display panel. By dichroic mirrors 103, white light emitted from a light source is separated into collimated color component rays 110, 111, and 112 of RGB and deflected to the light collecting plate 102 at different incident angles. Each microlens focuses the color component rays 110, 111, and 112 of RGB onto the apertures 107, 108, and 109 of corresponding RGB pixels in the liquid crystal display panel. Accordingly, the apertures 107, 108 and 109 of RGB pixels can receive the color component rays 110, 111, and 112, respectively. The color component rays 110, 111 and 112 are transmitted through the apertures 107, 108 and 109 and emitted therefrom as outgoing rays 115, 116 and 117. In this manner, color display can be performed without using a color filter. It thus follows that there is no loss of light due to the color filter. Therefore, the dimensions and the cost of the optical system can be reduced.
In the display device using such a microlens or hologram optical element plate, each microlens or hologram optical element must be precisely aligned with a corresponding set of color pixels of the liquid crystal display panel. To reduce loss of light, the precision of the alignment must be increased as the pixels of the liquid crystal display panel are downsized. This is particularly important to the above-described display device with no color filter. Conventionally, there is an attempt to adjust the positional relationship between the microlenses and the color pixels of the liquid crystal display panel by observing a moire pattern. However, in such a moire-based alignment method, it is difficult to secure the precision of alignment enough to cope with the downsizing of pixels. In addition, this method cannot determine the center of each microlens and which one of the color pixels opposes the center of the microlens. Accordingly, the method is not applicable to the above-described single-panel display device with no color filter.